Maintaining circuit switched continuity in an enhanced universal terrestrial radio access network

ABSTRACT

A method for implementing a fallback procedure from a packet switched (PS) radio access technology (RAT) to a circuit switched (CS) RAT is disclosed. A paging message is received at a wireless transmit/receive unit (WTRU) via the PS RAT, the paging message including a WTRU identifier and a domain indicator, wherein the domain indicator indicates whether the paging message is related to a service on the CS RAT. If the WTRU identifier in the paging message matches a stored identifier of the receiving WTRU, then a fallback procedure to the CS RAT is performed. The WTRU responds to the paging message using a CS RAT-based identifier assigned to the WTRU.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/088,397, filed Aug. 13, 2008, which is incorporated by reference asif fully set forth herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

A goal of the Third (3^(rd)) Generation Partnership Project (3GPP) LongTerm Evolution (LTE) program is to develop new technology, newarchitecture, and new methods in new LTE settings and configurations.These features are being developed to provide improved spectralefficiency, reduced latency, and better utilization of the radioresources. These features are intended to provide faster userexperiences, richer applications, and improved services, with less cost.

LTE is a Packet Switched (PS)-only radio technology. It is desirable tosupport backwards mobility with legacy Global System for MobileCommunications (GSM). For inter-working with legacy Circuit Switched(CS) networks, such as GSM, it was expected that IP Multimedia CoreNetwork Subsystem (IMS) networks would be deployed. Specifically, VoiceCall Continuity (VCC) was expected to be the technique used for handingover voice calls from LTE PS networks, using Voice over InternetProtocol (VoIP) techniques, to legacy CS networks. It would be desirableto de-couple IMS deployments from LTE deployments. In other words, itwould be desirable to initially use the currently deployed CSinfrastructure for voice calls, while deploying LTE for high-speed PSservices only. For this reason, it would be desirable for LTE to allow amulti-mode wireless transmit/receive unit (WTRU), such as with LTE andGSM and/or Wideband Code Division Multiple Access (WCDMA), use the LTEnetwork for high-speed PS data traffic while reverting to legacy CSnetwork for voice traffic, without necessarily using any IMS featuressuch as VCC.

When a WTRU attaches to the Evolved Packet System (EPS) over the E-UTRANnetwork, the Non Access Stratum (NAS) layer Attach message may include aCS fallback indicator to indicate to the network the need to attach theWTRU in the CS domain as well. The Mobility Management Entity (MME) maythen perform the attachment to the CS domain on behalf of the WTRU,before indicating that the process completed via the Attach Acceptmessage, as shown in FIG. 1. The Attach procedure for the CS fallback inEPS may be realized based on a combined General Packet Radio Service(GPRS)/International Mobile Subscriber Identifier (IMSI) Attachprocedure as specified in the 3GPP standard TS 23.060.

FIG. 1 is a flow diagram of a method 100 for performing an Attachprocedure. In the method 100, messages are exchanged between a WTRU 102,an MME 104, a mobile switching center/visitor location register(MSC/VLR) 106, and a home subscriber server (HSS) 108. The WTRU 102initiates the Attach procedure by transmitting an Attach Requestmessage, including parameters as specified in 3GPP standard TS 23.401and a CS fallback indicator, to the MME 104 (step 110). The CS fallbackindicator indicates that the WTRU 102 is capable of using CS fallbackand configured to use CS fallback.

The EPS Attach procedure is performed as specified in 3GPP standard TS23.401 (step 112). The VLR 106 is updated according to the combinedGPRS/IMSI Attach procedure in 3GPP standard TS 23.060 if the AttachRequest message includes a Combined Update indicator (step 114). The VLRnumber is derived from the Tracking Area Identity (TAT). The MME 104starts the location update procedure towards the new MS C/VLR uponreceiving the first Insert Subscriber Data message from the HSS 108.This operation marks the WTRU 102 as EPS-attached in the VLR 106.

The MME 104 sends a Location Update Request message, such as a newLocation Area Identity (LAI), IMSI, MME address, or Location UpdateType, to the VLR 106 (step 116). A new LAI is determined in the MME 104based on a mapping from the Tracking Area (TA). A mapped LAI may be toeither a GSM EDGE Radio Access Network (GERAN) or a UMTS TerrestrialRadio Access Network (UTRAN).

The VLR 106 creates an association with the MME 104 by storing the MMEaddress (step 118). The VLR 106 performs a location update procedure inthe CS domain (step 120). The VLR 106 responds to the MME 104 with aLocation Update Accept message, such as a VLR Temporary MobileSubscriber Identity (TMSI) (step 122). The MME 104 sends an AttachAccept message, including parameters as specified in 3GPP standard TS23.401, a Location Area Identity (LAI), and a VLR TMSI (if allocated),to the WTRU (step 124). The existence of a LAI (and a VLR TMSI, ifallocated) indicates a successful attachment to the CS domain.

FIG. 2 is a flow diagram of a method 200 for a WTRU terminating a callwhile in Idle mode. In the method 200, messages are exchanged between aWTRU 202, an eNB 204, a MME 206, a radio network controller (RNC) orbase station controller (BSC) 208, a MSC/VLR 210, a HSS 212, and agateway mobile switching center (GMSC) 214.

The method 200 begins with the GMSC 214 receives an initial addressmessage (IAM; step 220). The GMSC 214 retrieves the routing informationof the terminating WTRU by using the Send Routing Info (SRI) procedures(step 222). The GMSC 214 sends the IAM to the MSC 210 on the terminatingside (step 224).

The MME 206 receives a paging (IMSI, VLR TMSI, or Location Information)message from the MSC 210 over a SGs interface (step 226). The TMSI (orIMSI) received from the MSC 210 is used by the MME 206 to find theS-TMSI, which is used as the paging address on the radio interface. Ifthe location information is reliably known by the MME 206 (i.e., the MMEstores the list of TAs), the MME 206 pages the WTRU 202 in all the TAs.If the MME 206 does not have a stored TA list for the WTRU 202, the MME206 should use the location information received from the MSC to pagethe WTRU. If pre-paging is deployed, this procedure takes place beforestep 224, immediately after the MSC 210 receives the MAP_PRN messagefrom the HSS 212.

The MME 206 sends a paging message to each eNB 204 (step 228). Thepaging message includes a suitable WTRU identity (i.e., S-TMSI or IMSI)and a core network (CN) domain indicator that indicates which domain (CSor PS) initiated the paging message. In this case, the domain indicatoris set to “CS” by the MME 206. The eNB 204 pages the WTRU 202 (step230), and the paging message contains a suitable WTRU identity (i.e.,S-TMSI or IMSI) and a CN domain indicator.

The WTRU 202 establishes an RRC connection and sends an Extended ServiceRequest (CS fallback indicator) to the MME 206 (step 232). The WTRU 202indicates its S-TMSI in the RRC signaling. The Extended Service Requestmessage is encapsulated in RRC and 51 AP messages. The CS fallbackindicator indicates to the MME 206 that CS fallback for the WTRU 206 isrequired. The MME 206 sends 51 AP: Initial WTRU Context Setup (includingWTRU capabilities, CS fallback indicator, and other parameters) toindicate the eNB 204 to move the WTRU 202 to UTRAN/GERAN (step 234).

For the next action, there are two options, the choice depending onwhether the target RAT has PS handover (HO) capability or not. If thetarget RAT has PS HO capability, then upon receipt of the Initial WTRUContext Setup message with a CS fallback indicator, the eNB 204 mayoptionally solicit measurement reports from the WTRU 202 to determinethe target cell to which PS handover will be performed (step 236). A PShandover is then performed and as part of the PS handover, the WTRU 202receives a HO from E-UTRAN Command that may contain a CS fallbackindicator, which indicates to the WTRU 202 that the handover wastriggered due to a CS fallback request. If the HO from E-UTRAN Commandcontains a CS fallback indicator and the WTRU 202 fails to establish aconnection to the target RAT, then the WTRU 202 considers that the CSfallback has failed.

If the target RAT has no PS HO capability, then upon receipt of theInitial WTRU Context Setup message with a CS fallback indicator, the eNB204 may optionally solicit measurement reports from the WTRU 202 todetermine the target cell to redirect the WTRU 202 to (step 236). Afterthat, the eNB 204 releases the RRC Connection with redirectioninformation to change to a CS-capable RAT (including RAT, frequency, andcell information). As an option, the inter-RAT system information mightbe provided by the eNB 204 using the Network Assisted Cell Change (NACC)procedure for GERAN. In this case, the WTRU 202 receives in inter-RATcell change order that may contain a CS fallback indicator, whichindicates to the WTRU 202 that the cell change order was triggered dueto a CS fallback request. If the inter-RAT cell change order contains aCS fallback indicator and the WTRU 202 fails to establish a connectionto the target RAT, then the WTRU 202 considers that the CS fallback hasfailed.

If the WTRU 202 obtains the LA/RA information of the new UTRAN/GERANcell (e.g., based on the system information or redirection information)and the LA/RA of the new cell is different from the one stored in theWTRU 202, it performs a LA Update or a Combined RA/LA update procedureif the target system operates in Network Mode of Operation (NMO) I (step238). The WTRU 202 responds with a page response message to the MSC 210as follows.

If the target RAT is UTRAN or GERAN Iu mode, the WTRU 202 establishes anRRC connection and responds to the paging message in an RRC InitialDirect Transfer message. The CN domain indicator is set to “CS” in theInitial Direct Transfer message. When received at the RNC 208, thePaging Response message is sent in an RANAP Initial WTRU message to theMSC 210 (step 242).

If the target RAT is GERAN A/Gb mode, the WTRU 202 establishes an RRconnection by using the procedures specified in 3GPP TS 44.018 (i.e.,the WTRU 202 requests and is assigned a dedicated channel, where itsends a Set Asynchronous Balanced Mode (SABM) containing a layer 3Service Request message=PAGING RESPONSE to the BSS and the BSS respondsby sending a UA). After establishing the main signaling link asdescribed in 3GPP TS 44.018, the WTRU 202 enters either Dual TransferMode or Dedicated Mode and the CS call establishment procedurecompletes. When received at the BSC 208, the Paging Response message issent in a BSSAP COMPLETE LAYER 3 INFORMATION message to the MSC. The BSSshould be prepared to receive a PAGING RESPONSE even when acorresponding PAGING REQUEST has not been sent by this BSS. Also, theMSC 210 should be prepared to receive a paging response after arelatively long time from when the CS paging message was sent (step226).

In case the MSC serving the 2G/3G cell is the same as the MSC thatserved the WTRU 202 while camped on LTE, it stops the paging responsetimer and establishes the CS connection (step 244).

If the MSC that receives the paging response is different from the MSCthat sent the paging request and if the LA Update or Combined RA/LAUpdate was not performed, the MSC rejects the page response by releasingthe A/Iu-cs connection (step 246). The RNC/BSC 208 in turn releases theRRC/RR connection (step 248). The RRC/RR release triggers the WTRU 202to perform a LA Update (step 250) as follows. If the target systemoperates in Network Mode of Operation (NMO) I, then the WTRU 202performs a combined RA/LA Update. When the target system operates in NMOI, if the WTRU 202 is still in UTRAN/GERAN after the CS voice call isterminated and if a combined RA/LA Update has not already beenperformed, the WTRU 202 performs a combined RA/LA Update procedure. Thisprocedure is used to create a Gs association between the MSC/VLR 210 andthe SGSN and to release the SGs association.

If the target system operates in NMO II or III, then the WTRU 202performs a LA Update towards the MSC 210. The LA Update triggers theRoaming Retry for CS fallback procedure. When the target system operatesin NMO II or III, if the WTRU 202 is still in UTRAN/GERAN after the CSvoice call is terminated and if a LA Update has not already beenperformed, the WTRU 202 performs a LA Update procedure. This procedureis used to release the SGs association between the MSC/VLR 210 and theMME 206.

It is noted that if the WTRU is in Idle mode, then paging may beinitiated, because the network is not aware of the location andattachment status of the WTRU. If the WTRU is in Connected mode, meaningthat the WTRU is attached to the network, paging the WTRU is not neededand the network may easily reach the WTRU via a dedicated message. Oneexample of a dedicated message is a “CS service notification” message.

FIG. 3 is a flow diagram of a method 300 for the preparation phase of amobile originated (MO) call in active mode. In the method 300, messagesare exchanged between a WTRU 302, an eNB 304, a BSS 306, an MME 308, anMSC 310, a SGSN 312, and a serving GW 314. The WTRU 302 sends a CS CallRequest message to the eNB 304 (step 320). The eNB 304 may optionallyrequest a measurement report from the WTRU 302 to determine the targetGERAN/UTRAN cell to which PS handover will be performed (step 322).

When the WTRU 302 is moving, it may be necessary to handover the WTRU toa different eNB and/or BSS to maintain the connection between the WTRUand the network (i.e., perform a relocation process). The eNB 304 sendsa Relocation Required message to the MME 308 (step 324). The MME 308forwards a Relocation Request message to the SGSN 312 (step 326). TheSGSN 312 sends a PS Handover Request message to the BSS 306 (step 328).The SGSN 312 reserves radio resources in a target BSS (step 330) and thetarget BSS creates a Target BSS to Source BSS Transparent Container(step 332). The BSS 306 sends a PS Handover Request Acknowledge messageto the SGSN 312 (step 334). The SGSN 312 forwards a Relocation Responsemessage to the MME 308 (step 336). After this step is completed, theWTRU 302 has been handed over to the target BSS.

FIG. 4 is a flow diagram of a method 400 for the execution phase of a MOcall in active mode. In the method 400, messages are exchanged between aWTRU 402, an eNB 404, a BSS 406, an MME 408, an MSC 410, a SGSN 412, anda serving GW 414. Uplink and downlink payload PDUs are exchanged betweenthe WTRU 402 and the eNB 404, utilizing the serving GW 414 as needed(step 420). The MME 408 sends a Relocation Command to the eNB 404 (step422), which triggers the eNB 404 to send a Handover from E-UTRAN Commandto the WTRU 402 (step 424).

The WTRU 402 and the eNB 404 perform a GERAN A/Gb access procedure (step426) and the WTRU 402 sends an XID Response message to the BSS 406 (step428). The BSS 406 sends a PS Handover Complete message to the SGSN 412(step 430) and forwards the XID Response message to the SGSN 412 (step432). Also at this time, it is possible for the WTRU 402 to send uplinkpacket data to the eNB 404 (step 434).

If the target RAT is GERAN, the WTRU 402 sends a SABM message with aConnection Management (CM) Service Request to the BSS 406 (step 436).The BSS 406 forwards complete Layer 3 information along with the CMService Request to the MSC 410, which indicates that CS resources havebeen allocated in the GERAN cell (step 438). The BSS 406 responds to theWTRU 402 by sending a UA with the CM Service Request, which positivelyacknowledges the SABM message (step 440). The WTRU 402 then initiates aCS call establishment procedure (step 442).

Part of the processing of the Handover from E-UTRAN Command (step 424)includes the SGSN 412 receiving a Handover Complete message. Uponreceiving the Handover Complete message, the SGSN 412 sends a ForwardRelocation Complete message to the MME 408 to indicate completion of thePS handover procedure (step 444). The MME 408 responds to the SGSN 412by sending a Forward Relocation Complete Acknowledge message to the SGSN412 (step 446).

The SGSN 412 sends an Update PDP Context Request message to the servingGW, including a new SGSN address, a tunnel endpoint identifier (TEID),and a negotiated quality of service (QoS) (step 448) and optionallysends IP packets to the serving GW 414 (step 450). The serving GW 414updates the PDP context fields and sends an Update PDP Context Responsemessage (including the TEID) to the SGSN 412 (step 452). At this point,the serving GW 414 sends new incoming downlink IP packets to the SGSN412 instead of the source eNB (step 454). The downlink IP packets arethen forwarded to the BSS 406 (step 456) and ultimately to the WTRU 402(step 458).

The WTRU 402 and the SGSN 412 perform an XID negotiation procedure forLLC ADM (step 460). The WTRU 402 and the SGSN 412 may also perform anXID negotiation procedure for LLC ABM (step 462). It is noted that oneor both of the XID negotiation procedures (for ADM and ABM) may beperformed, depending on the LLC layer parameters to be negotiated. TheWTRU 402 triggers a routing area update procedure when it is possible tosend uplink data packets (step 464).

Even with the foregoing procedures, there are two problems that need tobe addressed: a combined location area update/tracking area update andthe identity of the WTRU that is used for paging.

1. Combined Location Area Update/Tracking Area Update

One problem relates to the combined Location Area Update (LAU)/TrackingArea Update (TAU) procedure necessary to remain attached to the CSdomain while in the E-UTRAN. In legacy GPRS, a routing area (RA) was asubset of a location area (LA). The system information would broadcastboth the location area identity (LAI) and the routing area identity(RAI). A change in LA implied a change in RA, but not vice versa. In LTESystem Information, there is no provision to broadcast the LA code ofthe surrounding legacy GSM/UMTS CS network. In addition, there is notsupposed to be a pre-defined relationship between TAs and LAs.Therefore, this problem may be stated: how does the WTRU determine thata combined TAU/LAU procedure needs to be triggered?

2. WTRU Identity for Paging

A second problem relates to the WTRU identity for paging. In LTE, theWTRU identity for paging is the S Temporary Mobile Subscriber Identity(S-TMSI). But the WTRU is not supposed to respond to paging messages viathe IMSI in LTE. In legacy GSM, the WTRU may be paged using either theTMSI or the IMSI.

In case the WTRU performed a combined EPS/IMSI Attach or a CombinedTAU/LAU procedure, the MSC/VLR would either assign a TMSI to the WTRU oruse the WTRU's IMSI for paging. A TMSI is unique only within the LAwhere it was assigned. Because there is no relationship between LAs andTAs, a WTRU may, in Idle Mode, cross LAs where the previously assignedTMSI may be invalid. FIG. 5 shows a conceivable scenario where the WTRU,while being in the same TA (TA1), crosses between two different LAs,such as LA1 and LA2, without performing a TA update procedure toward theMME. The problem in this situation is how to properly page the WTRU.

During the Attach procedure for connecting to LTE services (as shown inFIG. 1), the network must allocate an ID number to the WTRU (a GlobalUnique Temporary Identifier (GUTI) which includes the S-TMSI). Allpaging messages to the WTRU use the S-TMSI as the identifier for theWTRU. Under existing procedures, if the network pages the WTRU using theIMSI, the WTRU is supposed to detach from the network and then reattachto the network, to create the appropriate parameters in the network'sdatabase so that the WTRU may be paged using the IMSI. As one example,in GSM, the WTRU always has an IMSI and may also have a TMSI, ifassigned by the network. But, the VLR does not have to allocate a TMSIto the WTRU. In LTE, the MME must allocate a GUTI, which includes theS-TMSI. If the VLR does not allocate a TMSI to the WTRU, and sends backthe WTRU's IMSI in the Attach Accept message, then the WTRU must deleteany TMSI that it had stored. As a result, the WTRU may only be paged bythe IMSI. But if the WTRU may only be paged by the IMSI in the CSdomain, there is a problem, because in LTE, the WTRU cannot be paged bythe IMSI, and has to be paged by the S-TMSI.

SUMMARY

A WTRU may be paged by using the assigned IMSI. A bit may be added toexisting messaging to indicate that the CN domain is CS, so that theWTRU knows it is receiving a CS page using the IMSI. When the WTRU fallsback (i.e., leaves E-UTRAN) to GERAN or UTRAN, it must use the IMSI inthe paging response message to the MSC/VLR. In addition, the WTRUindicates a combined LAU/TAU when it is registered in both the PS andthe CS domains and the mobility management procedure for a tracking areaupdate has been triggered.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawings,wherein:

FIG. 1 is a signal diagram of an attach procedure for CS fallback;

FIG. 2 is a signal diagram of a method for a WTRU terminating a callwhile in Idle mode;

FIG. 3 is a signal diagram of the preparation phase of a MO call inactive mode;

FIG. 4 is a signal diagram of the execution phase of a MO call in activemode;

FIG. 5 is a diagram of an example relationship between location areasand tracking areas;

FIG. 6 shows an example wireless communication system including aplurality of wireless transmit/receive units (WTRUs) and an evolved NodeB (eNB);

FIG. 7 is an example functional block diagram of a WTRU and the eNB ofFIG. 6;

FIG. 8 is a flowchart of a method for triggering a combined TAU/LAUprocedure;

FIG. 9 is a flowchart of another method for triggering a combinedTAU/LAU procedure;

FIG. 10 is a flowchart of a method for triggering a LAU procedure;

FIG. 11 is a flowchart of a method for determining a paging identity fora WTRU;

FIG. 12 is a flowchart of a second method for determining a pagingidentity for a WTRU;

FIG. 13 is a flowchart of a third method for determining a pagingidentity for a WTRU; and

FIG. 14 is a flowchart of a fourth method for determining a pagingidentity for a WTRU.

DETAILED DESCRIPTION

When referred to hereafter, the term “wireless transmit/receive unit(WTRU)” includes, but is not limited to, a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the term “base station” includes, but is notlimited to, a Node B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

A person having ordinary skill in the art should understand that themethod and apparatus provided herein are applicable to any accesstechnology which uses circuit switched or packet switched data, such as3GPP LTE, WCDMA, GSM, GPRS, Enhanced Data for GSM Evolution (EDGE), CodeDivision Multiple Access (CDMA) 2000 (and related technologies), and theIEEE 802 family of technologies, for example 802.11, 802.16, and WiMAX.

FIG. 6 shows an example wireless communication system 600 including aplurality of WTRUs 610 and an eNB 620. As shown in FIG. 6, the WTRUs 610are in communication with the eNB 620. It should be noted that, althoughan example configuration of WTRUs 610 and an eNB 620 is depicted in FIG.6, any combination of wireless and wired devices may be included in thewireless communication system 600.

FIG. 7 is an example functional block diagram 700 of a WTRU 610 and theeNB 620 of the wireless communication system 600 of FIG. 6. As shown inFIG. 7, the WTRU 610 is in communication with the eNB 620.

In addition to the components that may be found in a typical WTRU, theWTRU 610 includes a processor 612, a receiver 614, a transmitter 616,and an antenna 618. The receiver 614 and the transmitter 616 are incommunication with the processor 612. The antenna 618 is incommunication with both the receiver 614 and the transmitter 616 tofacilitate the transmission and reception of wireless data. Theprocessor 612 is configured to perform a method of maintaining circuitswitched continuity in an E-UTRAN.

In addition to the components that may be found in a typical Node B, theNode B 620 includes a processor 622, a receiver 624, a transmitter 626,and an antenna 628. The receiver 624 and the transmitter 626 are incommunication with the processor 622. The antenna 628 is incommunication with both the receiver 624 and the transmitter 626 tofacilitate the transmission and reception of wireless data. Theprocessor 622 is configured to perform a method of maintaining circuitswitched continuity in an E-UTRAN.

Triggers for Performing a Combined TAU/LAU

The following triggers for performing a combined tracking area update(TAU)/location area update (LAU) may be used individually or in anycombination.

System Information Indication

The E-UTRAN system information may carry an indication of the LA of thesurrounding CS network, such as GSM or UMTS. This information may, forexample, be carried on E-UTRAN System Information Blocks, such as SIB1.The information may indicate whether the LA is valid for a GERAN networkor a UTRAN network. This information may indicate to the WTRU whether acombined TAU/LAU procedure is required in this area.

A WTRU that is currently in the E-UTRAN and in IDLE mode may initiate acombined TAU/LAU procedure when it detects a change in the LA broadcastby the System Information Block (SIB) in the E-UTRAN. FIG. 8 is aflowchart of a method 800 for triggering a combined TAU/LAU procedure.The method 800 begins with the WTRU receiving the LA of the surroundingCS network (step 802). A determination is made whether the WTRU iscurrently in the E-UTRAN (step 804). If the WTRU is not currently in theE-UTRAN, then the method terminates (step 806). If the WTRU is currentlyin the E-UTRAN, a determination is made whether the WTRU is in Idle mode(step 808). If the WTRU is not in Idle mode, then the method terminates(step 806). If the WTRU is in Idle mode, then a determination is madewhether the WTRU has detected a change in the LA (step 810). If the WTRUhas not detected a change in the LA, then the method terminates (step806). If the WTRU has detected a change in the LA, then the WTRUinitiates a combined TAU/LAU procedure (step 812) and the methodterminates (step 806).

Timer

The MSC/VLR may assign a timer to the WTRU when it performs an IMSIAttach procedure or a LAU Request procedure over the E-UTRAN. The timermay continue running in the NAS, even if the Evolved Packet SystemMobility Management (EMM) sub-layer is in EMM-Connected mode or inEMM-Idle mode, as long as the WTRU is registered in the EPS domain, theCS domain, or both. When the timer expires, the WTRU may initiate acombined TAU/LAU procedure.

FIG. 9 is a flowchart of method 900 for triggering a combined TAU/LAUprocedure. The method 900 begins with the WTRU performing an IMSI Attachprocedure or a LAU Request procedure over the E-UTRAN (step 902). Afterone of these procedures is performed, a timer is set by the MSC/VLR(step 904). Once the timer expires (step 906), the WTRU initiates acombined TAU/LAU procedure (step 908) and the method terminates (step910).

Subscriber Identity Module (SIM) Card

The MSC/VLR may inform the WTRU about a new LAI to be stored on theWTRU's SIM card via the MME without the WTRU initiating a LAU request.As an example, in connected mode, if the MME determines that the WTRU isin an area belonging to a different LAI than the last registered LA, itmay initiate the LAU on behalf of the WTRU. When doing so, the MME sendsthe new LAI and IMSI to the WTRU. The WTRU identity may be the TMSI, incase the MME creates and holds an association between the WTRU IMSI andthe TMSI. The network may then configure the WTRU with a new LAI (andoptionally a new TMSI) in any NAS message.

FIG. 10 is a flowchart of a method 1000 for triggering a LAU procedure.The method 1000 begins with the WTRU moving into an area with a new LAI(step 1002). The MME initiates an LAU procedure on behalf of the WTRU(step 1004). The MME sends the new LAI and new IMSI to the WTRU (step1006) and the method terminates (step 1008).

EPS/IMSI Attached

If the WTRU is EPS/IMSI attached and detects a condition for triggeringa TAU request, the WTRU combines the TAU request with a LAU request. Onecondition for triggering the TAU request is when the WTRU enters an areawhere the TAI is not in the list of TAs previously registered by theWTRU, meaning that the WTRU is entering a new area. When this occurs,the WTRU needs to perform a registration update, which is a combinedTAU/LAU procedure.

Paging Identity for the WTRU

The following techniques for determining a paging identity for the WTRUmay be used individually or in any combination.

IMSI/TMSI Mapping

The MME may keep a mapping between the IMSI, the TMSI (if allocated),and the corresponding S-TMSI. If the MS C/VLR initiates paging inE-UTRAN for MT services using the IMSI, the MME may map the IMSI to thecorresponding S-TMSI. The MME may then page the WTRU in E-UTRAN usingthe S-TMSI and an indication on the page message of the cause value,such as CS service, CS fallback, MT CS call, MT Short Message Service(SMS), etc. If the WTRU detects that the page message is directed to anidentity assigned by upper layers for the WTRU (a TMSI or an IMSI), itinitiates an Extended Service Request message on the E-UTRAN network,and sets the cause value for the service request to page response. Ifthe WTRU is re-directed (falls back) to GSM/UMTS CS, the WTRU sends apage response using the IMSI.

FIG. 11 is a flowchart of a method 1100 for determining a pagingidentity for a WTRU. The MME maintains a mapping between the IMSI, theTMSI, and the S-TMSI (if assigned; step 1102). The MSC/VLR initiatespaging of the WTRU in the E-UTRAN using the IMSI (step 1104). The MMEmaps the IMSI to the corresponding S-TMSI (step 1106). The MME pages theWTRU in the E-UTRAN using the S-TMSI and a cause value (step 1108). Adetermination is made at the WTRU whether the S-TMSI in the page messageis the receiving WTRU's S-TMSI (step 1110). In one embodiment, the WTRUcompares the S-TMSI in the page message with the S-TMSI stored at theWTRU, for example, on the Universal Subscriber Identity Module (USIM)card. If the S-TMSI in the page message is not the receiving WTRU'sS-TMSI, meaning that the page message is not intended for the receivingWTRU, then the page message is discarded (step 1112) and the methodterminates (step 1114).

If the S-TMSI in the page message is the receiving WTRU's S-TMSI (step1110), then the WTRU initiates an Extended Service Request message onthe E-UTRAN (step 1116). The WTRU then falls back to GSM or UMTS for theCS service (step 1118). After completing the fall back to CS, the WTRUsends a page response message using the IMSI (step 1120) and the methodterminates (step 1114).

IMSI Paging

If the MSC/VLR initiates paging in the E-UTRAN for MT services using theIMSI, the MME may page the WTRU in the E-UTRAN using the IMSI. If theWTRU detects that the cause for the page message is related to a CSservice, for example, CS fallback, a MT CS call, MT SMS, a CS domainindicator, etc., it may not ignore the page request nor detach from theE-UTRAN, but instead initiates an Extended Service Request message onthe E-UTRAN network, and sets the cause value for the service request topage response. If the WTRU is re-directed (falls back) to GSM/UMTS CS,the WTRU sends a page response using the IMSI.

FIG. 12 is a flowchart of a method 1200 for determining a pagingidentity for a WTRU. The method 1200 begins with the MSC/VLR initiatingpaging of the WTRU in the E-UTRAN using the IMSI (step 1202). The MMEpages the WTRU in the E-UTRAN using the IMSI (step 1204). The WTRUdetects a cause value associated with the page message (step 1206) anddetermines whether the page message is related to a CS service (step1208). The paging message includes a WTRU identifier (such as the IMSI)and a domain indicator (set to either CS or PS). If the page message isnot related to a CS service, meaning that the domain indicator is set toPS, then the WTRU reattaches to the E-UTRAN (step 1210) and the methodterminates (step 1212).

If the page message is related to a CS service, meaning that the domainindicator is set to CS (step 1208), then the WTRU initiates an ExtendedService Request message on the E-UTRAN (step 1214). The WTRU then fallsback to GSM or UMTS for the CS service (step 1216). After completing thefall back to CS, the WTRU sends a page response message using the IMSI(step 1218) and the method terminates (step 1212).

S-TMSI Paging

The MME may keep a mapping between the IMSI, TMSI (if allocated), andthe corresponding S-TMSI. If the MS C/VLR initiates paging in E-UTRANfor MT services using the TMSI, the MME map the TMSI to thecorresponding S-TMSI. The MME then pages the WTRU in the E-UTRAN usingthe S-TMSI and includes an indication on the page message of the causevalue, such as, CS service, CS fallback, a MT CS call, MT SMS, etc. Ifthe WTRU detects that the page message is directed to an identityassigned by upper layers for the WTRU, it initiates an Extended ServiceRequest message on the E-UTRAN network, and sets the cause value for theservice request to page response. If the WTRU is re-directed (fallsback) to GSM/UMTS CS, the WTRU sends a page response using the IMSI.

FIG. 13 is a flowchart of a method 1300 for determining a pagingidentity for a WTRU. The MME maintains a mapping between the IMSI, theTMSI, and the S-TMSI (if assigned; step 1302). The MSC/VLR initiatespaging of the WTRU in the E-UTRAN using the TMSI (step 1304). The MMEmaps the TMSI to the corresponding S-TMSI (step 1306). The MME pages theWTRU in the E-UTRAN using the S-TMSI and includes a cause value in thepage message (step 1308). A determination is made at the WTRU whetherthe S-TMSI in the page message is the receiving WTRU's S-TMSI (step1310). If the S-TMSI in the page message is not the receiving WTRU'sS-TMSI, meaning that the page message is not intended for the receivingWTRU, then the page message is discarded (step 1312) and the methodterminates (step 1314).

If the S-TMSI in the page message is the receiving WTRU's S-TMSI (step1310), then the WTRU initiates a Extended Service Request message on theE-UTRAN (step 1316). The WTRU then falls back to GSM or UMTS for the CSservice (step 1318). After completing the fall back to CS, the WTRUsends a page response message using the IMSI (step 1320) and the methodterminates (step 1314).

IMSI Paging

The MME may keep a mapping between the IMSI, TMSI (if allocated), andthe corresponding S-TMSI. If the MS C/VLR initiates paging in E-UTRANfor MT services using the TMSI, the MME maps the TMSI to thecorresponding S-TMSI. The MME then pages the WTRU in the E-UTRAN usingthe IMSI and includes an indication on the page message of the causevalue, for example, CS service, CS fallback, a MT CS call, MT SMS, etc.If the WTRU detects that the page message is directed to an identityassigned by upper layers for the WTRU, it may not ignore the pagerequest nor detach from E-UTRAN, but instead it initiates an ExtendedService Request message on the E-UTRAN network, and sets the cause valuefor the service request to page response. When the WTRU is re-directed(falls back) to GSM/UMTS CS the WTRU sends a page response using theIMSI.

FIG. 14 is a flowchart of a method 1400 for determining a pagingidentity for a WTRU. The MME maintains a mapping between the IMSI, theTMSI, and the S-TMSI (if assigned; step 1402). The MSC/VLR initiatespaging of the WTRU in the E-UTRAN using the TMSI (step 1404). The MMEmaps the TMSI to the corresponding IMSI (step 1406). The MME pages theWTRU in the E-UTRAN using the IMSI and includes a cause value in thepage message (step 1408). A determination is made at the WTRU whetherthe IMSI in the page message is the receiving WTRU's IMSI (step 1410).If the IMSI in the page message is not the receiving WTRU's IMSI,meaning that the page message is not intended for the receiving WTRU,then the page message is discarded (step 1412) and the method terminates(step 1414).

If the IMSI in the page message is the receiving WTRU's IMSI (step1410), then the WTRU initiates a Extended Service Request message on theE-UTRAN (step 1416). The WTRU then falls back to GSM or UMTS for the CSservice (step 1418). After completing the fall back to CS, the WTRUsends a page response message using the IMSI (step 1420) and the methodterminates (step 1414).

Although features and elements are described above in particularcombinations, each feature or element may be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method for implementing a fallback procedure from a packet switched(PS) radio access technology (RAT) to a circuit switched (CS) RAT,comprising: receiving a paging message at a wireless transmit/receiveunit (WTRU) via the PS RAT, the paging message including a WTRUidentifier and a domain indicator, wherein the domain indicatorindicates whether the paging message is related to a service on the CSRAT; determining whether the WTRU identifier in the paging messagematches a stored identifier of the receiving WTRU; performing a fallbackprocedure to the CS RAT on a condition that the WTRU identifier in thepaging message matches the stored identifier of the receiving WTRU; andresponding to the paging message using a CS RAT-based identifierassigned to the WTRU.
 2. The method according to claim 1, wherein theWTRU identifier in the paging message is an S-temporary mobilesubscriber identity.
 3. The method according to claim 1, wherein theWTRU identifier in the paging message is an international mobilesubscriber identity.
 4. The method according to claim 1, wherein theperforming includes sending a message in the PS RAT to indicate that theWTRU will fall back to the CS RAT.
 5. The method according to claim 1,wherein the CS RAT-based identifier is an international mobilesubscriber identity.
 6. The method according to claim 1, furthercomprising: discarding the paging message on a condition that the WTRUidentifier in the paging message does not match the stored identifier ofthe receiving WTRU.
 7. The method according to claim 1, furthercomprising: reattaching the WTRU to the PS RAT on a condition that theWTRU identifier in the paging message does not match the storedidentifier of the receiving WTRU.
 8. A wireless transmit/receive unit(WTRU), comprising: an antenna; a receiver in communication with theantenna; a transmitter in communication with the antenna; and aprocessor in communication with the receiver and the transmitter, theprocessor configured to: receive a paging message via a packet switched(PS) radio access technology (RAT), the paging message including a WTRUidentifier and a domain indicator, wherein the domain indicatorindicates whether the paging message is related to a service on acircuit switched (CS) RAT; determine whether the WTRU identifier in thepaging message matches a stored identifier of the WTRU; perform afallback procedure to the CS RAT on a condition that the WTRU identifierin the paging message matches the stored identifier of the WTRU; andrespond to the paging message using a CS RAT-based identifier assignedto the WTRU.
 9. The WTRU according to claim 8, wherein the WTRUidentifier in the paging message is an S-temporary mobile subscriberidentity.
 10. The WTRU according to claim 8, wherein the WTRU identifierin the paging message is an international mobile subscriber identity.11. The WTRU according to claim 8, wherein the processor is furtherconfigured to initiate the fallback procedure to the CS RAT by sending amessage in the PS RAT.
 12. The WTRU according to claim 8, wherein the CSRAT-based identifier is an international mobile subscriber identity. 13.The WTRU according to claim 8, wherein the processor is furtherconfigured to: discard the paging message on a condition that the WTRUidentifier in the paging message does not match the stored identifier ofthe WTRU.
 14. The WTRU according to claim 8, wherein the processor isfurther configured to: reattach the WTRU to the PS RAT on a conditionthat the WTRU identifier in the paging message does not match the storedidentifier of the WTRU.
 15. A method for implementing a fallbackprocedure from a packet switched (PS) radio access technology (RAT) to acircuit switched (CS) RAT, comprising: initiating paging a wirelesstransmit/receive unit (WTRU) in the PS RAT; sending a paging message tothe WTRU via the PS RAT, the paging message including a WTRU identifierand a domain indicator, wherein the domain indicator indicates whetherthe paging message is related to a service on the CS RAT; receiving afallback initiation message from the WTRU via the PS RAT; and receivinga paging response message from the WTRU, the paging response messageincluding a CS RAT-based identifier of the WTRU.
 16. The methodaccording to claim 15, wherein the WTRU identifier in the paging messageis an S-temporary mobile subscriber identity.
 17. The method accordingto claim 15, wherein the WTRU identifier in the paging message is aninternational mobile subscriber identity.
 18. The method according toclaim 15, wherein the CS RAT-based identifier is an international mobilesubscriber identity.
 19. The method according to claim 15, furthercomprising: maintaining a mapping between different identifiers assignedto the WTRU, wherein the WTRU may be paged by any known identifier. 20.A method for performing a combined tracking area update and locationarea update procedure at a wireless transmit/receive unit (WTRU),comprising: determining whether the WTRU is attached to a packetswitched radio access technology (RAT) and a circuit switched RAT;detecting a trigger condition for performing a tracking area update,wherein the trigger condition includes the WTRU entering an area where atracking area identifier of the entered area is not in a list oftracking areas previously registered by the WTRU; and performing acombined tracking area update and location area update procedure upondetecting the trigger condition.